1. Field of the Invention
The present invention relates to a method for hot shaping through solid-blank forming such as forging or rolling a workpiece or raw material of metal or of an intermetallic compound at a temperature of more than about 1000° C. The invention also relates to an agent for a coating to reduce the heat emission from a workpiece or raw material heated to deforming temperature.
2. Discussion of Background Information
With materials with poor deformation properties a hot forming of a workpiece of metal, such as an ingot or primarily formed raw material of metal or of intermetallic compounds to form a forging requires a precise temperature control from heating up to the removal of the part from the forming means.
A sufficient workability of the material of the workpiece is often given only in a narrow temperature window, because lower forming temperatures lead to a brittleness and higher temperatures likewise lead to a brittleness and/or to a coarse grain formation of the microstructure of the workpiece.
As the case may be, the limit of a sufficient workability is at high temperatures above 1000° C.
The emitted thermal energy increases in general with rising temperature to the fourth power so that with high surface temperatures of the workpiece the energy loss and the drop in temperature in the edge area in the unit of time are high.
With necessarily high forming temperatures it is therefore difficult and/or expensive to ensure a temperature with sufficient workability of the material also in the edge area of the workpiece over a necessary period of time.
Workpieces are heated to forming temperature in the usual manner in a furnace. The heated part is subsequently removed from the furnace with known means, conveyed to a shaping means, placed on a table roller or a die part and processed with dies in a forming manner. During this period of time the surface of the workpiece emits heat and/or heat is dissipated into the dies.
The general problem therefore lies in a rapid loss of temperature of the zone of the workpiece close to the surface and an occurrence of defects, such as cracks, resulting therefrom.
To solve this problem it has already been proposed and is also practiced once in a while to transfer the heated workpiece within a short period of time. However, it is usually not possible to position the heating unit and the forming device in immediate vicinity of each other.
Furthermore, an attempt has also already been made to heat the workpiece so much that even with a drop in temperature the surface zone thereof is still in the temperature range of the workability of the material. However, in this manner a coarsening and/or deterioration of the microstructure or center defects can occur.
Methods wherein the workpiece is enclosed in a capsule and is heated and deformed therein are also known. A method of this type can be rewarding with respect to a deformation of a part in a narrow temperature window, but requires a high expenditure.
In terms of process engineering, an isothermal forging of the workpiece is possible and useful in which the dies are heated to a temperature close to the forming temperature. However, a method of this type is extremely complex and expensive.
It would be advantageous to have available a method of the type mentioned at the outset for forming a workpiece, which method overcomes the disadvantages of the known methods.